Question

describe the difference between yield stress and ultimate stress of a steel element

Answer 1

When any steel element is under stress, it will undergo elongation i.e length of the element will increase due to ductile nature of the steel.Till one point elongation is directly proportional to the stress applied and element will go to its previous shape once we remove this stress(hook's law).

however after continuous stress,at one point steel will not obey hooks law,or it will have permanent deformation .So the stress at which steel starting yielding is called yield point.

If we are applying continuous stress ,maximum stress at which steel element will break,this is the ultimate stress limit of steel.

SO,

Yield stress is the stress at which that the material deforms permanently, ultimate tensile stress is the stress at which it breaks.

Ultimate Tensile Strength is a engineering important parameter when designing brittle material because there is no yield point. Whereas in designing ductile material, yield stress is a important parameter.

Hope you got the answer. Good luck